The purpose of this project is to define the humoral and cellular immune responses that relate to immunodiagnosis, immunopathology, and protective immunity of patients with lymphatic filariasis, onchocerciasis, and loiasis. Serodiagnosis of new or pre-patent onchocerciasis infections has been made feasible through the use of purified recombinant onchocercal antigen (OV16). Serologic assays for filarial infection based on IgG4 antibody detection have been shown to have enhanced specificity, but such antibodies require 6-9 months to develop despite the strong stimulation of chronic helminth infection. Histopathologic and serologic evidence implicates the eosinophil and its granule proteins as a primary determinant of post-treatment reactions n onchocerciasis and in pulmonary pathology of the Tropical Eosinophilia syndrome in bancroftian filariasis; IL-5 appears to be the primary mediator of the eosinophil responses. Populations with bancroftian filariasis or onchocerciasis have been examined to define immunologic parameters that distinguish "naturally immune" from infected animals. A 43kD protein from infective larvae that may be a protective immunogen for bancroftian filariasis has been cloned and sequenced; its practical usefulness is under further study. Similar studies in onchocerciasis have also identified several differentially recognized molecules that are being purified and evaluated.